Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/48—Electroplating: Baths therefor from solutions of gold

Definitions

• This invention relates to a gold electroplating bath, and more particularly to a gold electroplating bath containing an additive to permit the deposition of bright gold coatings at high speeds.
• the invention also relates to a process for the electrodeposition of gold using the bath.
• Gold is widely used as a contact material in the electronics industry, most usually in the form of a thin coating obtained by an electroplating process.
• the more important properties required of such a coating are low contact resistance, high corrosion resistance and good wear resistance.
• Gold electroplating baths which contain merely gold in an electrodepositable form and an electrolyte have been found to give coatings which are inadequate for use in contact applications in the electronics industry, principally because such coatings show insufficient resistance to abrasion.
• the quality of electrodeposited gold coatings can be improved by adding other materials to the gold plating bath.
• Such additives are often called “brighteners", because they increase the brightness of gold deposits obtained at a given current density.
• the brightness of a gold deposit is not itself of importance in most industrial applications, it has been found that the brightness of a gold coating is often a good guide to one or more aspects of coating quality, such as wear resistance and deposit structure.
• Transition metal salts such as cobalt, nickel and iron salts
• Gold electroplating baths which include these compounds have been found to give gold coatings of greatly improved wear resistance. For this reason, cobalt and nickel-containing acid gold electrolytes are widely used in the electronics industry.
• cobalt and nickel-containing acid gold electrolytes are widely used in the electronics industry.
• cobalt and nickel-brightened plating baths have been found to be lacking, because the maximum current density at which hard deposits can be obtained is relatively low.
• Attempts have been made to overcome this disadvantage by using higher concentrations of gold (typically 15 g/l instead of 8 g/l), but this substantially increases the cost of the process, and the improvement obtained is only slight.
• Certain organic compounds have also been used as additives in gold electroplating baths.
• One such compound is polyethyleneimine, as described in GB-A-No. 1453212. The effect of using this compound is to increase the maximum current density which can be employed, but the resultant coating is generally found to give poor wear resistance.
• GB-A-No. 1426849 discloses an electroplating bath which contains a metallic as well as an organic additive.
• the organic additives used are chemical compounds of sulphonic acids or sulphonic acid salts with heterocyclic nitrogen-containing hydrocarbons, such as pyridine sulphonic acid, quinoline sulphonic acid and picoline sulphonic acid.
• EP-A-No. 0150439 also discloses the use of substituted pyridine compounds for use as gold electroplating bath additives, and moreover discloses the use of substituted quinoline compounds.
• Preferred compounds are said to be mono- or dicarboxylic acid, mono- or disulphonic acid or mono- or dithiol derivatives of pyridine, and quinoline derivatives such as 3-quinoline carboxylic acid, 3-quinoline carboxaldehyde, and 2, 4-quinolinediol. Nicotinic acid (i.e.
• pyridine-3-carboxylic acid 2- or 4-pyridine carboxylic acid, nicotinic acid methyl ester, nicotinamide, nicotinic acid diethylamide, pyridine-2,3-dicarboxylic acid, pyridine-3,4-dicarboxylic acid, pyridine-3-sulphonic acid and pyridyl-4-thioacetic acid are said to be especially preferred.
• 3-(3-pyridyl) acrylic acid and 3-(3-quinolyl)acrylic acid are particularly effective additives for gold electroplating baths. They are more stable in use than the 3-amino pyridine which is disclosed in our European Patent Application No. 86300301.8, and they are superior to nicotinic acid in that they allow even higher current densities to be used while still obtaining bright coatings.
• the concentration of 3-(3-pyridyl) acrylic acid or 3-(3-quinolyl) acrylic acid used will depend on the particular electroplating conditions contemplated. If the concentration of additive is too low, a negligible brightening effect may be obtained. On the other hand, if the concentration of additive is too high, the cathodic efficiency may become unacceptably low. Generally speaking, a concentration of 3-(3-pyridyl) acrylic acid or 3-(3-quinolyl) acrylic acid in the range 0.01 g/l to 5 g/l will be found to be appropriate. A concentration of from 0.05 g/l to 1.0 g/l is preferred, and a concentration of from 0.2 g/l to 0.75 g/l is particularly preferred.
• the 3-(3-pyridyl) acrylic acid or 3-(3-quinolyl) acrylic acid may be used as free acids or as salts.
• Suitable salts are alkali metal salts such as the sodium and potassium salts.
• the gold electroplating bath of the present invention may include a metallic brightener, which can be any base metal or mixture of base metals which are known to be appropriate for use in acid gold electroplating baths. Included in such metals are cobalt, nickel, iron, chromium, cadmium, copper, zinc, tin, indium, manganese and antimony. Cobalt, nickel and iron are particularly preferred.
• the metallic brightener is generally used in the form of a water soluble salt, such as the sulphate, citrate or acetate, and may be used at a concentration of from 10 mg to 10 g/l.
• a water soluble salt such as the sulphate, citrate or acetate
• metal complexes with chelating agents such as ethylenediaminetetraacetic acid (EDTA) may be used.
• the concentration of metallic brightener is from 100 mg/l to 5 g/l, for example from 350 mg/l to 2 g/l.
• the gold of the electroplating bath of the invention is in the form of a water-soluble complex, such complexes being well known in the art.
• complexes are ammonium and alkali metal gold cyanides. Potassium gold cyanide is especially preferred.
• the gold complex will generally be present in the electroplating bath at a concentration of from 1 to 100 g/l, and preferably at a concentration of from 2 to 20 g/l, for example 4 or 8 g/l.
• the usual acid buffing systems may be used in the electroplating bath of the invention, to obtain a pH which is preferably in range 3.0 to 5.5.
• a citrate/oxalate buffer may be used to obtain a pH in the range 4 to 5, for example a pH of 4.5.
• electroplating bath of the present invention and a process for its use, are now illustrated further by the following Examples.
• This composition was used to plate brass sheets in a High-speed Hull cell, at a temperature of 50° C.
• Bright deposits (as defined in our European Patent Application No. 86300301.8) were obtained at current densities up to 10 A/dm 2 , and a cathodic efficiency of 42% was obtained even at a current density of 5 A/dm 2 .
• a barrel-plating solution comprising the following components was prepared:
• Example 2 was repeated using a citrate/oxalate buffer at pH 4.7, with the results given in Table II.
• Example 2 was repeated using cobalt (1 g/l as cobalt sulphate) instead of nickel with the results given in Table III.
• Example 3 was repeated using cobalt (1 g/l as cobalt sulphate) instead of nickel. The results shown in Table IV were obtained.
• Example 6 was repeated using a High-speed Hull Cell, and similar results were obtained, except that no significant improvement in maximum current density was obtained by increasing the concentration of 3-(3-pyridyl) acrylic acid beyond 0.5 g/l. At this concentration, the maximum current density at which bright coatings could be obtained was 6.5 A/dm 2 .

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Transition And Organic Metals Composition Catalysts For Addition Polymerization (AREA)
• Building Environments (AREA)
• Residential Or Office Buildings (AREA)
• Electrolytic Production Of Metals (AREA)

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Citations (5)

• 1986
  • 1986-05-21 GB GB868612361A patent/GB8612361D0/en active Pending
• 1987
  • 1987-05-11 FI FI872065A patent/FI872065A/fi not_active Application Discontinuation
  • 1987-05-19 DK DK252987A patent/DK168303B1/da active IP Right Grant
  • 1987-05-19 AT AT87304445T patent/ATE68835T1/de not_active IP Right Cessation
  • 1987-05-19 EP EP87304445A patent/EP0246869B1/de not_active Expired - Lifetime
  • 1987-05-19 DE DE8787304445T patent/DE3773990D1/de not_active Expired - Lifetime
  • 1987-05-19 ES ES198787304445T patent/ES2026910T3/es not_active Expired - Lifetime
  • 1987-05-20 KR KR870004986A patent/KR870011277A/ko not_active Application Discontinuation
  • 1987-05-20 NO NO872114A patent/NO872114L/no unknown
  • 1987-05-20 JP JP62121429A patent/JPS62287094A/ja active Pending
• 1988
  • 1988-01-11 US US07/144,607 patent/US4767507A/en not_active Expired - Lifetime
• 1991
  • 1991-10-24 GR GR91400797T patent/GR3002980T3/el unknown
• 1992
  • 1992-02-19 SG SG161/92A patent/SG16192G/en unknown
  • 1992-08-06 HK HK585/92A patent/HK58592A/xx not_active IP Right Cessation

Patent Citations (6)

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